Cub listens to audio of Scar rambling when he gets overstimulated by noise.
The sculk gave Cub amazing hearing (he will always hear your sneak attacks and know exactly where you're hiding), but it's incredibly overstimulating, and he hates 'being rewarded for becoming a monster'. He tried to get rid of it by damaging his hearing, until Scar noticed and tipped Impulse off on him similar noise-cancelling earbuds to the ones Ren uses for his dog-hearing for his birthday.
Now Cub wears them whenever he needs to focus, or when he has to handle huge crowds or many loud noises at once. He used to listen to music, but after being calmed so much by the comfort room, Scar recorded over 200 hours of yapping about space, and how safe/wonderful Cub is, with more coming every single week, just for Cub.
Cub absolutely loves them, but once Grian found them by accident and almost went insane after hearing just 3 minutes of it.